[Simon Lloyd]

The Author would have to custom that for you as there isn't that option to send it to whichever thread the user of the form chooses, unless you can use stuff like you can in the title like this:
Check the checkbox for which thread to post to and then put {q_1} so question one on your form would be a textbox for a thread id, this is only a guess, give it a go, if not you'll have to wait for the author to answer